Background:
Asthma, defined as “a chronic lung disorder that is marked by recurring episodes of airway obstruction...manifested by labored breathing accompanied especially by wheezing and coughing...” is a tremendously prevalent disease. Asthma already affects 300 million people worldwide and has a growing rate of 50% per decade. Studies have estimated the total cost of asthma in the U.S. alone to be between $2.3 and $7.2 billion US dollars per year, and summing across the globe asthma incurs greater total costs than HIV/AIDS and tuberculosis combined. Daytime symptoms are not, however, the whole story; many asthmatics experience a marked exacerbation of symptoms such as cough and wheeze at night, causing significant reductions in quantity and quality of sleep. This phenomenon, dubbed Nocturnal Asthma (NA), is thought to affect between 47-75% of asthmatics worldwide, though its prevalence is difficult to quantify. Current methods for diagnosing NA include:
Recently, other methods of quantifying asthma symptoms have been researched, which incorporate EMG, piezoelectric sensors, accelerometers, and microphones. The great majority of these clinical monitors focus on patient coughs. In addition to being the “dominant feature of asthma exacerbations,” cough frequency is strongly correlated to airway inflammation and has even been proposed to be a more sensitive measure of inflammation than simple spirometry. Interestingly, the cough frequencies of non-asthmatics, stable asthmatics without nocturnal asthma symptoms, and chronic coughers all decrease drastically between 2 and 5 AM. There is a distressing contrast between these findings and the disproportionate number of asthma deaths and respiratory arrests that happen at night. This indicates a distinction between NA and other manifestations of asthma, and that the presence of NA likely reflects improperly treated asthma. Need:
Most asthma monitors under development currently focus on performing clinical or diagnostic functions and are not suitable for home monitoring because they require trained clinicians to operate and interpret the results. The remaining fully automated systems fail to offer long-term, nighttime monitoring because they constrain the person's sleep with wires and sensors that were developed for ambulatory use. According to a number of studies those suffering from NA are more likely to suffer from:
Current Solutions:
Few commercial monitors exist and none target nocturnal asthma in children. By far, the most common are peak flow meters. While inexpensive (less than $40) these typically measure peak expiratory flow alone. While a digital solution called the Microlife can provide an additional measure of FEV1 (the volume of air forcibly exhaled in one second), it still cannot provide continuous monitoring or be used by a sleeping person. A commercial wheeze monitor called AirSonea was recently developed, though it is not yet available in the United States. It is a handheld sensor that determines if a user is wheezing once it is held to his/her neck for thirty seconds. While this could technically be used on a sleeping child, the parent would need to be awake already. The device also costs $150 dollars and must be paired with a smartphone to function. There are two ambulatory continuous monitoring solutions that are currently under development. The first is called VitaloJAK and is worn on the hip like a Holter monitor. It promises to detect coughs over periods of 24 hours with 98% sensitivity through a single sensor placed on the user’s chest. Due to its design, however, the product is intended for elderly patients who require continuous at-home respiratory monitoring due to COPD or severe asthma. The second solution is a smartphone application called the Automated Device for Asthma Monitoring (ADAM) that aims to measure coughs and wheezes using the phone’s microphone and accelerometers. During clinical trials, it recognized 7/10 coughs and incorrectly labeled 2 coughs/hour. It could not accurately monitor wheezes. |